After installing Qt 5.2-rc1 the icon was present until I have restarted my machine. After that I have tried to reinstall Qt 5.2-rc1, but with no luck. This problem was present in all past Qt5.* series and there are plenty other issues reported, but mainly for Unity desktop. I have tested this problem on Unity, Gnome3 (gnome-shell), LXDE, Xfce.